In phased radar arrays, it is often desirable to control the power level of the received/transmitted signal at each element of the array. It is further desirable to control the power level at each array element with high accuracy over a large signal range and across a wide bandwidth. In addition, it is desirable that each incremental design element in a radio frequency (RF) channel have as little degradation in performance as possible while minimizing the effect of phase shifts in the incoming or outgoing signal.
Variable gain amplifiers (VGAs) have conventionally used a single level of control. For example, a VGA is described in the co-pending commonly owned patent application Ser. No. 13/306,674 filed on Nov. 29, 2011, which is incorporated by reference as if fully set forth herein. A series of differential transistor pairs are connected in parallel to steer current through the VGA circuit to control gain. The performance requirements for these VGAs has increased and calls for greater gain range and smaller gain states (i.e. finer control), in addition to operation at higher frequencies. Thus, improvements to existing designs are needed. To increase gain range, for example, multiple VGAs may be arranged in stages so that the output of a first VGA in the chain serves as the input to a next VGA circuit. However, this solution requires additional space to accommodate multiple VGA circuits, as well as creating additional power requirements. In addition, as higher gain is realized, the input signal experiences some amount of compression. Compression of the input signal is cascaded through the system, thereby being exacerbated by each progressive VGA stage. Alternative circuits and methods are desired.